Apparatus for obtaining synthetic foam materials

ABSTRACT

In the production of a foam plastics material by a transfer injection process, the transfer nozzle is withdrawn from the foaming chamber as it injects plasticized material into that chamber so that the newly injected material does not compress previously injected material and, until the foaming is complete, there is no movement of the material in the foaming chamber apart from its expansion during foaming. The transfer nozzle directs material against the walls of the foaming chamber. It is valved so that a return movement of the nozzle into the foam chamber can expel foamed material from that chamber.

United States Patent 1 1 Staerman [111 1 3,774,811 [451 Nov. 27, 1973APPARATUS FOR OBTAINING SYNTHETIC FOAM MATERIALS 22 Filed: Dec.6, 197121 Appl. No.: 205,131

France 424/245 France 425/244 Primary ExaminerRobert B. Reeves AssistantExaminerDavid A. Scherbel Att0rneyMerriam, Marshall, Shapiro & Klose 5 7ABSTRACT [30] Foreign Application Priority Data Dec. 10, 1970 France7044491 In the production of a foam plastics material y a I h 52 US. Cl222 190, 222/229, 425/244 g i s:g ggslgz gfizzi i ggt fgfiz 51 Im. C182% 3/00 g 1 p clzed material mto that chamber so that the newly m- [58]Field of Search 425/4, 244, 245, t d It a] d t l t d 425/817 222/190 355229 394- 239/567 343 e coinpless prev'ousy e material and, until thefoaming is complete, there IS no References Cited movement of thematerial n the foaming chamber apart from its expansion dunng foaming.The transfer UNITED STATES PATENTS nozzle directs material against thewalls of the foaming 1,995,215 3/ 1935 Mehisen et a1. 239/343 X chamber.It is valved so that a return movement of the 3,007,202 1 1/1961 wuchernozzle into the foam chamber can expel foamed mate- 3,163,693 12/1964Steuger 425/245 X rial from that chamber.

FOREIGN PATENTS OR APPLICATIONS I 6,636 6/ 1962 Japan 425/244 3 Claims,3 Drawing Figures VARIABLE MIANS chamber within the foaming vessel.

BACKGROUND OF THE INVENTION The present invention concerns a method andan apparatus for obtaining synthetic foam materials.

In known transfer injection processes, the synthetic material mixed witha foaming agent is put into a first vessel called a plasticising vesseland containing a plasticising chamber where it is plasticised withoutfoaming, after which the plasticised material is transferred, through anozzle, into a second vessel called a foaming vessel and containing thefoaming chamber where it is foamed. It is then injected, for exampleinto moulds.

Until now apparatuses for carrying out this process have had seriousdisadvantages because the synthetic material, at the moment of transferfrom the plasticizing chamber to the foaming chamber, presses againstthefoam already formed or forming in the foaming chamber. Unless it doesthis it cannot get into the foaming chamber. The result of this is thatthe foaming of the incident synthetic material is notcarried out undergood conditions; also the foam already formed, because it has to movebecause of the action of this incident material, is made denser andsticks to the walls of the foaming vessel. Lastly, the incident materialmust foam under atmospheric pressure.

SUMMARYOF THE INVENTION The presentinvention does away with thesedisadvantages by arranging that plasticised synthetic material, mixedwith a foaming agent, is introduced through the transfer nozzle into afoaming chamber in such a way that each portion of foamed material isformed in a specific spot, reserved for it, in the said foaming chamberwhich is then under reduced pressure.

Thus, the foam is not, as in the known method, formed in a single place(close to the transfer nozzle) in the foaming vessel, then pressed on bythe subsequently incident matter. Also this foam fomrs at a time whenthe foaming vessel is under reduced pressure, and does not have to fightagainst atmospheric pressure.

In order to carry out the process according to the in- I vention, anapparatus can have a plasticising vessel in the form of a piston actingwith a cylindrical foaming vessel, a transfer nozzle borne by the saidplasticising vessel allowing it to communicate with the foaming Thuswhen the plasticising vessel retreats from the foaming chamber, areduced, pressure is created andbecause the transfer nozzle is thenopen, the plasticised material is introduced into the foaming chamber,the foam created being put thereinvsuccessively to that previouslycreated.

Preferably, the transfer nozzle is a valve nozzle allowing the foam tobe directed, not onto the previously introduced'foam, but in thedirection of the inside walls of the foaming vessel. If the foam beingformed is projected onto the foam already formed, it spoils the latter.In addition, if the foam is directed onto the walls, they then form asupport away from which the foam can develop freely towards the insideof the foaming chamber.

Advantageously the foaming vessel has an injection nozzle for the finalexpulsion of the foam from the apparatus and injection into e.g. a mouldwhich is closed during the retreat of the plasticising vessel and theformation of the foam and which is open after foam forample ofembodiment of the invention.

mation in order to allow for injection of foam through it under theinfluence of the movement of the plasticising vessel towards theinjection nozzle.

In an advantageous manner of embodying the invention, the plasticisingvessel carries with it a feed apparatus for synthetic material to beplasticised, for example an endless screw, and the retreating movementof the plasticising vessel from the foaming chamber is linked with themovement of the feed apparatus in such a way that the quantity of foamformed at the transfer nozzle corresponds to the free space left in thefoaming chamber by the retreat of the plasticising vessel. It can beseen that, by regulating the relationship between the movement of thefeed apparatus and the retreating movement of the piston, it is possibleto alter the density of the foam obtained.

The Figures of the attached drawing shows In this drawing:

FIG. 1 is a longitudinal schematic section of the apparatus.

FIG. 2 is a sectional view of an enlarged scale of the transfer nozzleof the apparatus in FIG. 1.

FIG. 3 is a section along the line IIIIII of FIG. 2. g The apparatusshown in FIG. 1 has an elongated plasticising vessel 1, ending in apiston head 2 coacting with a cylindrical foaming vessel 3, which actsas a cylinder in fluid-tight sliding relation with the head 2. Theinside,

of the plasticising vessel 1 can be put into communication with thefoaming chamber within the foaming vessel 3 means of avalved transfernozzle 4.

The plasticising vessel 1 has an endless feed screw 5, which isrotatable and is also mounted axially movably and is subjected (in knownmanner) to a plasticising counterp ressure indicated by the arrow F. Ahopper 6 allows for a synthetic material for plasticising to be brought,with a foaming agent, to the screw 5. A plasticising chamber 7 isdefined in variable manner in the vessel 1, between the transfer nozzle4 and the end of the screw 5. In the chamber material is plasticisedwithout foaming.

The foaming vessel 3 is closed, at its end opposite the vessel 1, by anend wall 8 in which is mounted an injection nozzle 9 provided with aclosure valve. Heating jackets l0 and 16 surround respectively thefoaming vessel 3 and the plasticising vessel 1,- whilst the latter issurrounded, at its end remote from the head 2, by cooling jackets 17 forcooling the material to be plasticised in that region, which thenprevents back flow of the plasticised material.

The transfer nozzle 4, mounted on the head 2 ,of the piston andcoaxially with the centre axis of the piston and cylinder, has acylindrical crown 11 also co-axial with the cylinder 3 and pierced byregularly spacedapart holes 12. This nozzle communicates with theplasticising chamber 7 by means of a narrow duct 13 which can be closedby a ball 14, urged towards such closure by a spring 15.

The making of foam material with the apparatus shown in the Figurestakes place, in accordance with the invention in the following way.

Let us assume that first the injection nozzle 9 is closed and that thepiston head 2 is near the said nozzle. A synthetic material to beplasticised is introduced,

one 6X- with a foaming agent, into the hopper, 6 and taken by the screwinto the plasticising chamber 7, the transfer nozzle 4 being closed. Thesynthetic material is therefore plasticised under known conditions andaccumulated in the chamber 7 and when the pressure of the plasticisedmaterial becomes greater under the action of the screw 5 than thatexerted by the spring on the ball 14, the latter is pushed back againstthe action of the spring, and allows the plasticisedmaterial to flowthrough the duct 13 and the holes 12 into the foaming vessel 3. Theshape of the nozzle 4, with its crown 11, is such that the material isdirected towards and onto the wall of the cylinder which forms thefoaming vessel 3. Thus the wall acts as a support for the foamedmaterial as it expands into the free space left in the radially centralportion of the chamber 3.

Simultaneously, the plasticising vessel 1 retreats within the vessel 3,that is to say the piston head 2 moves away from the nozzle 9, whichremains closed. The plasticised material escaping through the holes 12is thrown out, into the vessel 3, behind the foam already forrned, andits forming is aided by the reduced pressure created in the foamingchamber inthe vessel 3 by the movement of the vessel 1.

The apparatus according to the invention includes means (not shown) forsynchronisation of the movement of the screw 5 and of the retreatingmotion of the vessel 1, in such a way that the quantity of foam formedat the exit of the nozzle 4 corresponds to the volumne of the spacecreated, in the vessel 3, by the retreat of the vessel 1. Thus the foamissuing from the nozzle 4 is deposited into a part of the foamingchamber which is, as it were, reserved for it and in which it does notmove, except, for its expansion while foaming, until the final expulsionof the foamed material from the foaming chamber. 1

When the pressure of the plasticised mass in the chamber 7 gets less,the transfer nozzle 4 closes, that is to say that the ball 14 once againcloses the duct 13.

.The vessel 1 is then given a motion towards the injection nozzle 9. Thefoam formed in the vessel 3 is thus pressed against this nozzle 9 whichopens. To this end, this nozzle 9 can be of the valve type. The foam isthen injected through the nozzle 9.

After the injection of this foam it is possible to begin again the cyclewhich has just been described.

It can likewise be seen, that if the linkage between the retreatingmovement of the piston 2 and the movement of the screw 5 is adjustable,it is possible to alter the density of the foam obtained in the vessel3.

I claim:

1. Apparatus comprising:

a plasticizing chamber, in a plasticizing vessel, in the shape of apiston, in which a synthetic material is plasticized without foaming,

a foaming vessel with a foaming chamber in the shape of a cylindercoacting with said piston,

means to supply the plasticizing chamber with synthetic material, thismeans being carried by the plasticizing vessel,

A transfer nozzle between the plasticizing chamber and the foamingchamber through which plasticized material can be transferred from thechamber to the foaming chamber in which it is foamed,

means to increase the volume of the foaming chamber while moving thetransfer nozzle in the foaming chamber to deposit foamed syntheticmaterial in successive positions in the foaming chamber; and

means to decrease the volume of the foaming chamber to expel] foamtherefrom while maintaining the volume of the plasticizing chamberconstant.

2. Apparatus according to claim 1 wherein the transfer nozzle is anozzle urging the foam in the direction of the wall of the foamingvessel.

3. Apparatus according to claim 2 wherein the transfer nozzle has acylindrical crown with axis parallel to that of the piston and cylinderand provided with holes spaced over its surface, this crown being linkedto the plasticising chamber by a valved duct, and wherein the foamingvessel has an injection nozzle adapted to be closed during the retreatof the plasticising vessel and the formation of the foam and to be open,after the formation of the latter, whereby a reduced pressure may cisingvessel towards the said injection nozzle.

1. Apparatus comprising: a plasticizing chamber, in a plasticizingvessel, in the shape of a piston, in which a synthetic material isplasticized without foaming, a foaming vessel with a foaming chamber inthe shape of a cylinder coacting with said piston, means to supply theplasticizing chamber with synthetic material, this means being carriedby the plasticizing vessel, A transfer nozzle between the plasticizingchamber and the foaming chamber through which plasticized material canbe transferred from the chamber to the foaming chamber in which it isfoamed, means to increase the volume of the foaming chamber while movingthe transfer nozzle in the foaming chamber to deposit foamed syntheticmaterial in successive positions in the foaming chamber; and means todecrease the volume of the foaming chamber to expell foam therefromwhile maintaining the volume of the plasticizing chamber constant. 2.Apparatus according to claim 1 wherein the transfer nozzle is a nozzleurging the foam in the direction of the wall of the foaming vessel. 3.Apparatus according to claim 2 wherein the transfer nozzle has acylindrical crown with axis parallel to that of the piston and cylinderand provided with holes spaced over its surface, this crown being linkedto the plasticising chamber by a valved duct, and wherein the foamingvessel has an injection nozzle adapted to be closed during the retreatof the plasticising vessel and the formation of the foaM and to be open,after the formation of the latter, whereby a reduced pressure may beinduced in the foaming chamber during retreat of the plasticising vesseland the formed foam may be injected by means of the displacement of thesaid plasticising vessel towards the said injection nozzle.